Scheduling timing design for a tdd system

ABSTRACT

Disclosed is a method of transmitting, from an enhanced Node B (eNB), an indication of an uplink/downlink (UL-DL) subframe configuration of a scheduling cell and a scheduled cell in a wireless time-division duplex (TDD) system. Embodiments include identifying the type of the UL-DL subframe configuration of the scheduling cell and determining a UL-DL subframe configuration to use for UL resource allocation of the scheduled cell. Other embodiments include identifying a reference UL-DL subframe configuration to use for UL resource allocation of the scheduled cell.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. Provisional PatentApplication No. 61/612,188, filed Mar. 16, 2012, entitled “ADVANCEDWIRELESS COMMUNICATION SYSTEMS AND TECHNIQUES,” the entire disclosure ofwhich is hereby incorporated by reference.

FIELD

Embodiments of the present invention relate generally to the field ofcommunications, and more particularly, to selection of acknowledgementtiming in wireless communication networks.

BACKGROUND INFORMATION

A time division duplex (TDD) system, in wireless communications, mayoffer flexibility in resource utilization. For example, a TDD system mayuse different subframe configurations to match uplink and downlinktraffic characteristics of a wireless communications cell. Theflexibility of using different subframe configurations, may permit theratio between available uplink (UL) and downlink (DL) resources to rangefrom 3UL:2DL to 1UL:9DL.

Release 10, of 3^(rd) Generation Partnership Project's (3GPP) long-termevolution-advanced (LTE-A) communications standard, may limit support ofthe aggregation of TDD Component Carriers (CCs) to the sameuplink/downlink (UL-DL) subframe configurations. While such limitationsmay have simplified the design and operation within the standard, suchlimitations may have limited potential for greater data throughput.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are illustrated by way of example, and notby way of limitation, in the figures of the accompanying drawings inwhich like reference numerals refer to similar elements.

FIG. 1 schematically illustrates a wireless communication network inaccordance with various embodiments.

FIG. 2 schematically illustrates an optional hybrid adaptive repeat andrequest (HARQ) signal scheduling diagram in accordance with variousembodiments.

FIG. 3 schematically illustrates an optional HARQ signal schedulingdiagram in accordance with various embodiments.

FIG. 4 is a flowchart illustrating selection of a HARQ signal schedulingconfiguration in accordance with various embodiments.

FIG. 5 schematically illustrates an optional HARQ signal schedulingdiagram in accordance with a first method of various embodiments.

FIG. 6 schematically illustrates an optional HARQ signal schedulingdiagram in accordance with a first method of various embodiments.

FIG. 7 is a flowchart illustrating selection of a HARQ signal schedulingconfiguration in accordance with various embodiments.

FIG. 8 is a table illustrating an optional HARQ configuration selectionin accordance with a second method of various embodiments.

FIG. 9 schematically illustrates an optional HARQ signal schedulingdiagram in accordance with a second method of various embodiments.

FIG. 10 is a table illustrating another optional HARQ configurationselection in accordance with the second method of various embodiments.

FIG. 11 schematically depicts an example system in accordance withvarious embodiments.

DESCRIPTION OF THE EMBODIMENTS

Illustrative embodiments of the present disclosure include, but are notlimited to, methods, systems, and apparatuses for selection ofacknowledgement signal timing in a wireless communication network.

Embodiments include methods of identifying a UL-DL subframeconfiguration of a scheduling and scheduled cell in a TDD wirelesssystem utilizing cross-carrier scheduling. In some embodiments, a typeof the scheduling cell may be identified, for example based on a ULround trip time (RTT) of a HARQ process, and a UL-DL subframeconfiguration for UL resource allocation may be determined based atleast in part on the type of the scheduling cell. In other embodiments,a reference configuration may be used for the UL resource allocation.The reference configuration may be based at least in part on the UL-DLsubframe configurations of the scheduling and scheduled cells. In someembodiments the methods may be performed by an eNB, a UE, or throughsome combination of signaling between the two.

Various aspects of the illustrative embodiments will be described usingterms commonly employed by those skilled in the art to convey thesubstance of their work to others skilled in the art. However, it willbe apparent to those skilled in the art that some alternate embodimentsmay be practiced using with portions of the described aspects. Forpurposes of explanation, specific numbers, materials, and configurationsare set forth in order to provide a thorough understanding of theillustrative embodiments. However, it will be apparent to one skilled inthe art that alternate embodiments may be practiced without the specificdetails. In other instances, well-known features are omitted orsimplified in order to not obscure the illustrative embodiments.

Further, various operations will be described as multiple discreteoperations, in turn, in a manner that is most helpful in understandingthe illustrative embodiments; however, the order of description shouldnot be construed as to imply that these operations are necessarily orderdependent. In particular, these operations need not be performed in theorder of presentation.

The phrase “in one embodiment” is used repeatedly. The phrase generallydoes not refer to the same embodiment; however, it may. The terms“comprising,” “having,” and “including” are synonymous, unless thecontext dictates otherwise. The phrase “A/B” means “A or B”. The phrase“A and/or B” means “(A), (B), or (A and B)”. The phrase “at least one ofA, B and C” means “(A), (B), (C), (A and B), (A and C), (B and C) or (A,B and C)”. The phrase “(A) B” means “(B) or (A B)”, that is, A isoptional.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a wide variety of alternate and/or equivalent implementations maybe substituted for the specific embodiments shown and described, withoutdeparting from the scope of the embodiments of the present disclosure.This application is intended to cover any adaptations or variations ofthe embodiments discussed herein. Therefore, it is manifestly intendedthat the embodiments of the present disclosure be limited only by theclaims and the equivalents thereof.

As used herein, the term “module” may refer to, be part of, or includean Application Specific Integrated Circuit (ASIC), an electroniccircuit, a processor (shared, dedicated, or group) and/or memory(shared, dedicated, or group) that execute one or more software orfirmware programs, a combinational logic circuit, and/or other suitablecomponents that provide the described functionality.

FIG. 1 schematically illustrates a wireless communication network 100 inaccordance with various embodiments. Wireless communication network 100(hereinafter “network 100”) may be an access network of a 3GPP long-termevolution (LTE) or LTE-A network such as evolved universal mobiletelecommunication system (UMTS) terrestrial radio access network(E-UTRAN). The network 100 may include a base station, e.g., enhancednode base station (eNB) 104, configured to wirelessly communicate with amobile device or terminal, e.g., user equipment (UE) 108. Whileembodiments of the present invention are described with reference to anLTE network, some embodiments may be used with other types of wirelessaccess networks.

eNB 104 may include a receiver module 120 with which to receive signalsfrom UE 108 via one or more antennas 130. eNB 104 may include atransmitter module 124 with which to transmit signals to UE 108 via oneor more antennas 130. eNB 104 may also include a processor module 128coupled between receiver module 120 and transmitter module 124 andconfigured to encode and decode information communicated by the signals.

In embodiments in which the UE 108 is capable of utilizing carrieraggregation (CA), a number of CCs may be aggregated for communicationbetween the eNB 104 and the UE 108. In an initial connectionestablishment, the UE 108 may connect with a primary serving cell(PCell) of the eNB 104 utilizing a primary CC. This connection may beused for various functions such as security, mobility, configuration,etc. Subsequently, the UE 108 may connect with one or more secondaryserving cells (SCells) of the eNB 104 utilizing one or more secondaryCCs. These connections may be used to provide additional radioresources. In some embodiments the UE 108 may connect with as many asfour SCells.

Each CC may support a number of communication channels according to arelease of the 3GPP LTE-A communication standard. For example, each CCmay support a physical downlink shared channel (PDSCH) for transmissionof downlink data. As another example, each CC may support physicaluplink control channel (PUCCH) and/or physical uplink shared channel(PUSCH) to carry information between UE 108 and eNB 104. A CC mayinclude a plurality of uplink and downlink subframes for carryinginformation between eNB 104 and UE 108. A single 10 ms radio frame mayinclude ten subframes.

The CCs may be configured to transport information according to a TDDcommunication protocol. Each CC may be scheduled to transport data to UE108 or transport data to eNB 104 according to one of several UL-DLsubframe configurations. In some embodiments the UL-DL subframeconfigurations may be 3GPP LTE UL-DL subframe configurations 0-6 for ULTDD HARQ processes as defined in table 4.2-2 of 3GPP TS 36.211 v10.5.0(2012-06) shown in Table 1. In other embodiments, different UL-DLsubframe configurations may be used.

With reference to Table 1, each CC may be assigned to transport dataand/or control signals according to one of several possible UL-DLsubframe configurations. In this embodiment, a primary CC and secondaryCC may both be configured with the same UL-DL subframe configuration orwith different UL-DL subframe configurations. In general, each ofsubframes 0-9 that is labeled with a “D” or an “S” is a subframe withwhich UE 108 receives data from eNB 104, and each of subframes 0-9 thatis labeled with a “U” is a subframe through which UE 108 transmits datato eNB 104.

TABLE 1 TDD UL-DL Subframe Configurations Uplink-downlinkDownlink-to-Uplink Subframe number configuration Switch-pointperiodicity 0 1 2 3 4 5 6 7 8 9 0 5 ms D S U U U D S U U U 1 5 ms D S UU D D S U U D 2 5 ms D S U D D D S U D D 3 10 ms  D S U U U D D D D D 410 ms  D S U U D D D D D D 5 10 ms  D S U D D D D D D D 6 5 ms D S U U UD S U U D

In some embodiments, the UE 108 may be configured to communicate data tothe eNB 104, for example on the PUSCH. In response the eNB 104 maycommunicate an acknowledgement signal to the UE 108, for example throughthe physical hybrid adaptive repeat and request indicator channel(PHICH). According one embodiment, the acknowledgement signals may beHARQ signals corresponding to a positive acknowledgement (ACK) ofreceipt of data and a negative acknowledgement (NACK) of receipt ofdata. In embodiments, the eNB 104 may be configured to transmit ACK orNACK signals to notify the UE 108 that transmitted data has or has notbeen received, respectively.

eNB 104 may further be configured to determine a schedule with which totransmit ACK/NACK signals to UE 108. For example, eNB 104 may beconfigured to determine which UL-DL subframe configurations will be usedfor the PCell and the SCell, and transmit indications of the UL-DLsubframe configurations to the UE 108. In some embodiments, theindications of the UL-DL subframe configurations may be transmitted tothe UE 108 in a control signal which may be referred to as a systeminformation block (SIB). In some embodiments the control signal mayspecifically be the first system information block (SIB1) as describedin the 3GPP LTE standards. The SIB1 may be broadcast by the eNB 104, andcorrespondingly received by the UE 108, on the PDSCH.

UE 108 may include a receiver module 144, a transmitter module 148, aprocessor module 152, and one or more suitable antennas 156. Receivermodule 144 and transmitter module 148 may be coupled to one or moresuitable antennas 156 to transmit and receive wireless signals to/fromeNB 104.

Processor module 152 may be coupled to receiver module 144 andtransmitter module 148 and be configured to decode and encodeinformation transmitted in signals communicated between the UE 108 andthe eNB 104. Processor module may include a communication module 154 anda HARQ module 158. Processor module 152 may be configured to usecommunication module 154 to transmit information in uplink subframes ofthe PCell, e.g., on CC_0, according to the scheduling of a first UL-DLsubframe configuration at a first frequency. Processor module 152 mayalso be configured to transmit information in uplink subframes of theSCell, e.g., on CC_1, according to a second UL-DL subframe configurationat a second frequency that is different from the first frequency.According to one embodiment, the difference between transmissionfrequencies of CC_0 and CC_1 may range from hundreds of kilohertz totens of Gigahertz, in accordance with inter-band carrier aggregation. Insome embodiments, processor module 152 may use HARQ module 158 to selectHARQ timing sequence or timing schedules based on one of the UL-DLsubframe configurations of PCell or SCell.

Similarly, the processor module 128 of eNB 104 may be coupled with acommunication module 162 and a HARQ module 166. Processor module 128 maybe configured to use communication module 162 to transmit information indownlink subframes of the PCell and/or SCell, as described above withrespect to the uplink subframes of processor module 152.

As will be described in more detail hereafter, processor module 128 maybe configured to selectively transmit ACK/NACK information for SCellcommunications via a UL-DL subframe configuration that is different thanthe UL-DL subframe configuration of SCell. In embodiments, processormodule 128 may use HARQ module 166 to select a HARQ timing sequence ortiming schedule based on one of the UL-DL subframe configurations. HARQmodule 166 may also generate the ACK/NACK information for processormodule 128. The HARQ module 166 may be coupled with the communicationmodule 162 and may be configured to use the communication module 162 totransmit the generated ACK/NACK information via the selected HARQ timingsequence.

An advantage of a TDD system may be flexible resource utilizationthrough the use of different UL-DL subframe configurations such as theconfigurations 0-6 described above. The UL-DL subframe configurationsmay be selected to achieve higher efficiencies for uplink and downlinktraffic in a cell. As shown above in Table 1, the ratio betweenavailable UL and DL resources can range from 3UL:2DL in configuration 0to 1UL:9DL as shown in configuration 5. In some embodiments it may bedesirable for different UL-DL subframe configurations to be used ondifferent cells. For example, the PCell may use a differentconfiguration from the SCell. The use of different UL-DL subframeconfigurations may offer benefits such as legacy system coexistence,heterogeneous network (HetNet) support, aggregation of traffic-dependentcarriers, flexible configurations where a greater number of UL subframesare available for better coverage in lower bandwidth uses while a highernumber of DL subframes are available for higher bandwidth uses, and ahigher peak rate.

In embodiments where CA is used, cross-carrier scheduling may beperformed. In general, the cross-carrier scheduling may involve anindication that one serving cell is a scheduling cell, and anotherserving cell is a scheduled cell. For example, the PCell may be thescheduling cell, and the SCell may be the scheduled cell. In otherembodiments where the cell contains multiple SCells, a first SCell maybe a scheduling cell and a second SCell may be a scheduled cell. Inthese embodiments, the scheduled cell may be used to transmit data fromthe UE 108 to the eNB 104, and the scheduling cell, for example thePCell, may be used to transmit the HARQ ACK/NACK information from theeNB 104 to the UE 108. This specification will continue to discussembodiments with regard to the terms scheduling cells and scheduledcells.

In these embodiments where cross-carrier scheduling is used, the use ofdifferent UL-DL subframe configurations may impact the spectrumefficiency of uplink resources. This is because the 3GPP LTEspecifications may require at least four subframes between the UL datatransmission and the corresponding DL ACK/NACK transmission. However,resource utilization of UL subframes in the scheduled cells may not beperfectly efficient because the scheduling and scheduled cells may usedifferent UL-DL subframe configurations and therefore have differentscheduling timing. Scheduling timing may refer to the specific timingand configuration of UL, DL, or S subframes within a radio frame for thecell as directed by the UL-DL subframe configuration of the cell. If thescheduling timing of the scheduling and scheduled cells are different,then the subframe of the scheduling cell may be a UL subframe whereasthe same subframe of the scheduled cell may be a DL subframe, or viceversa, as discussed below in further detail. A UL transmission on thescheduled cell according to one UL-DL subframe configuration, forexample from the UE 108, may therefore not have a corresponding DLsubframe for an ACK/NACK transmission in the scheduling cell, forexample from the eNB 104.

An example of inefficient UL resource utilization due to differentscheduling timing between the scheduled and scheduling cells is shown inFIG. 2. The UL-DL subframe configuration of the scheduling cell may beconfiguration 6, and include three normal DL subframes D, two specialsubframes S, and five UL subframes U. The UL-DL subframe configurationof the scheduled cell may be configuration 4 and include seven normal DLsubframes D, one special subframe S, and two UL subframes U. If thePUSCH scheduling timing of the UL-DL subframe configuration of thescheduled cell, e.g. configuration 4, is used for PUSCH transmission onthe scheduled cell in this embodiment, then only UL subframe 3 on thescheduled cell could be used for uplink data transmission.Correspondingly, ACK/NACK information could only be received on subframe9 of the scheduling cell, as indicated by the solid arrow. Subframe 2may be unusable because the corresponding scheduling subframe on thescheduling cell may be a UL subframe rather than a DL subframe, e.g.subframe 8 on the scheduling cell as shown in FIG. 2, and consequentlyUL grant/PHICH information associated with subframe 2 may not betransmitted. Therefore, only subframe 3 may be usable, which may reduceUL resource efficiency of the scheduled cell by 50%. Differentembodiments and combinations may have similar, greater, or lesserresource efficiency reductions.

An alternative method may be to use the scheduling timing of the UL-DLsubframe configuration of the scheduling cell, as shown in FIG. 3.However, as shown in FIG. 3, the UL data transmission from the scheduledcell in subframe 3 may be processed by the scheduling cell, and thescheduling cell may send a DL ACK/NACK transmission in subframe 0 of thenext radio frame, as shown by the solid line. However, as indicated bythe dashed line, the next available UL transmission for non-adaptiveretransmission triggered by NACK information in the PHICH channel, forexample NACK information transmitted when the eNB 104 does not receive adata transmission from the UE 108 correctly, may begin at subframe 4according to the scheduling timing of the scheduling cell. In thisembodiment where the timing of the scheduling cell is used, however,subframe 4 may be a DL subframe and therefore not be usable for asubsequent UL data transmission, as indicated by the dashed line. Inthis embodiment, the next available UL subframe may not be untilsubframe 2 of the following radio frame. This delay in the HARQ processmay undesirably decrease the efficiency of UL resource utilization.

FIG. 4 depicts a flowchart of a method for coordinating the UL-DLsubframe configurations and increasing uplink efficiency ofcross-carrier scheduled TDD cells for a UL HARQ process according to oneembodiment. In this method the UL-DL subframe configuration of ascheduling cell is identified at 400. The UL-DL subframe configurationof a scheduled cell is then identified at 405. It will be understoodthat the identification at 400 and 405 may occur sequentially orsubstantially simultaneously. After identifying the UL-DL subframeconfiguration of the scheduling and scheduled cells, the UL RTT of thescheduling cell may be identified at 410. The UL RTT may be the timethat it takes a HARQ process to occur. Some UL-DL subframeconfigurations may have an RTT of 10 milliseconds (ms). Specifically,UL-DL subframe configurations such as configurations 1, 2, 3, 4, and 5may have an RTT of 10 ms. These configurations may be designated “Type1” configurations at 415. Other UL-DL subframe configurations, forexample configurations 0 or 6, may have an RTT of between 10 to 13 msand be designated “Type 2” configurations at 415. The designations of“Type 1” or “Type 2” are arbitrary names, and the names of the types maybe different in different embodiments. The designations stated abovewill be used for the remainder of the specification, however it will beunderstood that different names may be used in alternative embodimentsof the method described herein.

If the UL-DL subframe configuration of the scheduling cell is designatedas Type 1, then the scheduling timing of the HARQ process may follow theUL-DL subframe configuration of the scheduling cell at 420.Alternatively, if the UL-DL subframe configuration of the schedulingcell is designated as Type 2, then the scheduling timing of the HARQprocess may follow the UL-DL subframe configuration of the scheduledcell at 425. Alternative embodiments may have additional types or waysof determining the different types of the UL-DL subframe configurations.

In some embodiments, the method of FIG. 4 may be performed by an eNB104, and in other embodiments the method may be performed by a UE 108.In certain embodiments, the method may be performed by both the UE 108and the eNB 104 so that both entities are able to independentlydetermine which UL-DL subframe configuration to use for UL-DLtransmission in the HARQ process. In other embodiments, the UE 108 mayperform the method and then transmit a signal to the eNB 104 whichinstructs the eNB 104 as to which UL-DL subframe configuration to usefor UL-DL transmission in the HARQ process. Alternatively, the eNB 104may perform the method and then transmit a signal to the UE 108 whichinstructs the UE 108 which UL-DL subframe configuration to use for UL-DLtransmission in the HARQ process. If the method is being performed bythe UE 108, then the UE 108 may identify the UL-DL subframeconfigurations of the scheduling cell at 400 and the scheduled cell 405by receiving and analyzing an SIB1 from the eNB 104 as described above.

As shown in FIG. 5, use of the method shown in FIG. 4 may increaseuplink resource efficiency. In this embodiment, the scheduling cell maybe using a UL-DL subframe configuration such as configuration 1, and thescheduled cell may be using a UL-DL subframe configuration such asconfiguration 2. As noted above with respect to 415, both configurations1 and 2 may be designated as Type 1 configurations. Therefore, accordingto 415 and 420, the scheduling and scheduled cells may use the UL-DLsubframe configuration of the scheduling cell, i.e. configuration 1.

As shown in FIG. 5, using the UL-DL subframe configuration of thescheduling cell, configuration 1, the scheduled cell is able to transmitUL data in subframe 2 from the UE 108 to the eNB 104 and receive acorresponding ACK/NACK signal from the eNB 104 on the DL in subframe 6of the scheduling cell. A separate HARQ process may be able to transmitUL data from the UE 108 to the eNB 104 in subframe 7 and receive acorresponding ACK/NACK signal from the eNB 104 in subframe 1 of the nextradio frame of the scheduling cell.

An alternative embodiment is shown in FIG. 6. In FIG. 6 the schedulingcell may be using a UL-DL subframe configuration such as configuration0, and the scheduled cell may be using a UL-DL subframe configurationsuch as configuration 1. As noted above with respect to 415,configuration 0 may be designated a Type 2 configuration andconfiguration 1 may be a Type 1 configuration. Therefore, according to415 and 425, the scheduling and scheduled cells may use the UL-DLsubframe configuration of the scheduled cell, configuration 1.

As shown in FIG. 6, the scheduled cell is able to transmit UL data fromthe UE 108 to the eNB 104 in subframe 2, and receive a correspondingACK/NACK signal from the eNB 104 in subframe 6 of the scheduling cell. Aseparate HARQ process may also be performed wherein the UE 108 transmitsUL data in subframe 7 of the scheduled cell and receives a correspondingACK/NACK signal from the eNB 104 in subframe 1 of the next radio frameof the scheduling cell.

The embodiments described above with respect to FIGS. 5 and 6 areexamples. Alternative embodiments may follow the logic of the methoddescribed in FIG. 4 with respect to different combinations of UL-DLsubframe configurations.

FIG. 7 depicts a method of an alternative embodiment for increasinguplink efficiency in a HARQ process of cross-carrier scheduled TDDcells. The UL-DL subframe configurations of a scheduling and scheduledcell may be identified at 700 and 705, respectively. A reference UL-DLsubframe configuration may then be identified at 710. In someembodiments, the reference UL-DL subframe configuration may be the sameas the UL-DL subframe configuration of the scheduling cell. In otherembodiments the reference UL-DL subframe configuration may be the sameas the UL-DL subframe configuration of the scheduled cell. In stillother embodiments the reference UL-DL subframe configuration may bedifferent from the UL-DL subframe configuration of either the schedulingor scheduled cell. In some embodiments, multiple reference UL-DLsubframe configurations may be identified.

In general, the reference UL-DL subframe configuration may be identifiedat 710 through comparison of the UL-DL subframe configuration of thescheduling cell and the UL-DL subframe configuration of the scheduledcell. Specifically, if the method is being performed by an eNB 104, thenthe eNB 104 may compare the UL-DL subframe configurations of thescheduling cell and the scheduled cell against a table which may bestored in a memory of the eNB 104. In some embodiments the table may bestored on a server or other device communicatively coupled with the eNB104. The table may identify a reference UL-DL subframe configurationbased on one or both of the UL-DL subframe configurations of thescheduling and scheduled cells. The eNB 104 may then communicate thereference UL-DL subframe configuration to a UE 108 via RRC signaling.

In an alternative embodiment, the UE 108 may receive an indication ofthe UL-DL subframe configurations of the scheduling cell and thescheduled cell from the eNB 104, for example as information in a SIB1received in a signal on the PDSCH, as described above. The UE 108 maythen consult a table which compares one or both of the UL-DL subframeconfigurations of the scheduling and scheduled cells to determine whichreference UL-DL subframe configuration to use for a HARQ process. Insome embodiments the table may be stored in a memory of the UE 108. Inother embodiments, the table may be stored on another device such as anexternal memory or a server that is communicatively coupled with the UE108.

FIG. 8 depicts an exemplary embodiment of a table that may be used todetermine a reference UL-DL subframe configuration for a HARQ processaccording to the method described above in FIG. 7. Specifically, thefirst column of the table in FIG. 8 depicts a UL-DL subframeconfiguration of a scheduling cell. The second column of the table inFIG. 8 depicts a UL-DL subframe configuration of a scheduled cell. Thethird column of the table in FIG. 8 depicts a reference UL-DL subframeconfiguration that may be used for the UL-DL subframe configurations ofthe scheduling and the scheduled cell.

In the embodiment of FIG. 8, the reference UL-DL subframe configurationis 6 if the UL-DL subframe configuration of the scheduling cell is 0 andthe UL-DL subframe configuration of the scheduled cell is 1, 3, 4, or 6,or if the UL-DL subframe configuration of the scheduling cell is 1 andthe UL-DL subframe configuration of the scheduled cell is 3 or 6; thereference UL-DL subframe configuration is 1 if the UL-DL subframeconfiguration of the scheduling cell is 0 and the UL-DL subframeconfiguration of the scheduled cell is 2 or 5, or if the UL-DL subframeconfiguration of the scheduling cell is 1 and the UL-DL subframeconfiguration of the scheduled cell is 4 or 5; the reference UL-DLsubframe configuration is the scheduled cell configuration if the UL-DLsubframe configuration of the scheduling cell is 2 and the UL-DLsubframe configuration of the scheduled cell is 3, 4, or 6; thereference UL-DL subframe configuration is 5 or 1 if the UL-DL subframeconfiguration of the scheduling cell is 2 and the UL-DL subframeconfiguration of the scheduled cell is 5; the reference UL-DL subframeconfiguration is 1 if the UL-DL subframe configuration of the schedulingcell is 6, and the UL-DL subframe configuration of the scheduled cell is1, 2, 4, or 5; the reference UL-DL subframe configuration is 6 if theUL-DL subframe configuration of the scheduling cell is 6 and the UL-DLsubframe configuration of the scheduled cell is 3; the reference UL-DLsubframe configuration is 0 if the UL-DL subframe configuration of thescheduling cell is 3 or 4, and the UL-DL subframe configuration of thescheduled cell is 0; the reference UL-DL subframe configuration is 6 ifthe UL-DL subframe configuration of the scheduling cell is 3 and theUL-DL subframe configuration of the scheduled cell is 1, or if the UL-DLsubframe configuration of the scheduling cell is 3 or 4 and the UL-DLsubframe configuration of the scheduled cell is 6; and the referenceUL-DL subframe configuration is 1 or 6 if the UL-DL subframeconfiguration of the scheduling cell is 4 and the UL-DL subframeconfiguration of the scheduled cell is 1, or if the UL-DL subframeconfiguration of the scheduling cell is 3 or 4 and the UL-DL subframeconfiguration of the scheduled cell is 2.

The fourth column of the table in FIG. 8 depicts uplink resourceefficiencies that may be achieved by using the reference configurationsshown in this embodiment. For example, if the UL-DL subframeconfiguration of the scheduling cell is equal to 0 and the UL-DLsubframe configuration of the scheduled cell is equal to 1, then theremay be 75% uplink resource efficiency, or 75% of the UL subframes of theUL-DL subframe configuration 1 of the scheduled cell may be usable for aHARQ process. Similarly, if the UL-DL subframe configuration of thescheduled cell is equal to 6 and the UL-DL subframe configuration of thescheduled cell is equal to 1, then the uplink resource efficiency mayalso be 75%. In the present embodiment if the UL-DL subframeconfiguration of the scheduling cell is equal to 0 and the UL-DLsubframe configuration of the scheduled cell is equal to 3, then theuplink resource efficiency may be 66%. In the other combinations ofUL-DL subframe configurations of the scheduling and scheduled cells ofthe present embodiment, the uplink resource efficiency may be as high as100%. In other embodiments the uplink resource efficiency may be higheror lower for different combinations, dependent on which reference UL-DLsubframe configuration is used.

FIG. 9 depicts the use of a UL-DL subframe configuration of a referencecell according to one embodiment. In this embodiment the UL-DL subframeconfiguration of the scheduling cell is 0. The UL-DL subframeconfiguration of the scheduled cell is 2. As indicated by the table ofFIG. 8, the reference UL-DL subframe configuration may then be 1. Asshown in FIG. 9, the UE 108 may transmit UL data in subframe 2 of thescheduled cell and, using the reference UL-DL subframe configuration,receives a DL ACK/NACK signal in subframe 6 of the scheduling cell fromthe eNB 104. A separate HARQ process may also occur wherein the UE 108transmits UL data in subframe 7 of the scheduled cell and receives a DLACK/NACK signal in subframe 2 of the following radio frame of thescheduling cell. In this embodiment it can be seen that 100% of the ULresources of the scheduled cell may be utilized, as indicated by thetable of FIG. 8.

FIG. 10 depicts another exemplary embodiment of a table that may be usedto determine a reference UL-DL subframe configuration for a HARQ processaccording to the method described above in FIG. 7. Specifically, thefirst column of the table in FIG. 10 depicts a plurality of sets ofreference UL-DL subframe configurations, dependent on the UL-DL subframeconfiguration of the scheduling cell and scheduled cell. The secondcolumn depicts a UL-DL subframe configuration of a scheduling cell. Thethird column of the table in FIG. 10 depicts a UL-DL subframeconfiguration of a scheduled cell. The fourth column of the table inFIG. 10 depicts a reference UL-DL subframe configuration that may beused for the determination of the PUSCH HARQ timing for the scheduledcell.

In the first set, the reference UL-DL subframe configuration is equal to1 if the UL-DL subframe configuration of the scheduling cell is equal to1 and the UL-DL subframe configuration of the scheduled cell is equal to2, 4, or 5; the reference UL-DL subframe configuration is equal to 2 ifthe UL-DL subframe configuration of the scheduling cell is equal to 2and the UL-DL subframe configuration of the scheduled cell is equal to5; the reference UL-DL subframe configuration is equal to 3 if the UL-DLsubframe configuration of the scheduling cell is equal to 3 and theUL-DL subframe configuration of the scheduled cell is equal to 4 or 5;and the reference UL-DL subframe configuration is equal to 4 if theUL-DL subframe configuration of the scheduling cell is equal to 4 andthe UL-DL subframe configuration of the scheduled cell is equal to 5.

In the second set, the reference UL-DL subframe configuration is equalto 6 if the UL-DL subframe configuration of the scheduling cell is equalto 1, 2, 3, or 4, and the UL-DL subframe configuration of the scheduledcell is equal to 6; the reference UL-DL subframe configuration is equalto 0 if the UL-DL subframe configuration of the scheduling cell is equalto 3 or 4, and the UL-DL subframe configuration of the scheduled cell isequal to 0; and the reference UL-DL subframe configuration is equal to 1if the UL-DL subframe configuration of the scheduling cell is equal to 4and the UL-DL subframe configuration of the scheduled cell is equal to1.

In the third set, the reference UL-DL subframe configuration is equal to3 if the UL-DL subframe configuration of the scheduling cell is equal to2 and the UL-DL subframe configuration of the scheduled cell is equal to3; and the reference UL-DL subframe configuration is equal to 4 if theUL-DL subframe configuration of the scheduling cell is equal to 2 andthe UL-DL subframe configuration of the scheduled cell is equal to 4.

In the fourth set, the reference UL-DL subframe configuration is equalto 0 if the UL-DL subframe configuration of the scheduling cell is equalto 6 and the UL-DL subframe configuration of the scheduled cell is equalto 0; the reference UL-DL subframe configuration is equal to 1 if theUL-DL subframe configuration of the scheduling cell is equal to 0 or 6,and the UL-DL subframe configuration of the scheduled cell is equal to1, 2, or 5; the reference UL-DL subframe configuration is equal to 3 ifthe UL-DL subframe configuration of the scheduling cell is equal to 0 or6, and the UL-DL subframe configuration of the scheduled cell is equalto 3; the reference UL-DL subframe configuration is equal to 6 if theUL-DL subframe configuration of the scheduling cell is equal to 0 andthe UL-DL subframe configuration of the scheduled cell is equal to 6;and the reference UL-DL subframe configuration is equal to 4 if theUL-DL subframe configuration of the scheduling cell is equal to 6 andthe UL-DL subframe configuration of the scheduled cell is equal to 4.

The method of FIG. 7 may use a single set, for example only set 1 asshown in the table of FIG. 10, or the method may use a combination oftwo or more of the sets to identify the reference UL-DL subframeconfiguration at 710. In some embodiments, additional combinations ofreference UL-DL subframe configurations, UL-DL subframe configurationsof the scheduling cell, and UL-DL subframe configurations of thescheduled cell, not shown in FIG. 10, may be used in combination withthose shown above in FIG. 10. For example, additional embodiments mayinclude reference UL-DL subframe configurations for combinations of theUL-DL subframe configurations of the scheduling and scheduled cell whichare not shown in FIG. 8 or 10.

It will be noted that the table of FIG. 10 contains elements of both themethod of FIG. 4 and the table of FIG. 8. For example, the table of FIG.10 depicts the use of the UL-DL subframe configuration of the schedulingcell as a reference UL-DL subframe configuration if the UL-DL subframeconfiguration of the scheduling cell is a Type 1 configuration asdescribed above at element 420 of FIG. 4. For example, the table of FIG.10 indicates that a UL-DL reference configuration of 1 may be used ifthe UL-DL subframe configuration of the scheduling cell is 1 and theUL-DL subframe configuration of the scheduled cell is 2. Similarly, FIG.10 depicts the use of the UL-DL subframe configuration of the scheduledcell as a reference UL-DL subframe configuration if the UL-DL subframeconfiguration of the scheduled cell is a Type 2 configuration asdescribed above at element 425 of FIG. 4. For example, the table of FIG.10 indicates that a UL-DL reference configuration of 4 may be used ifthe UL-DL subframe configuration of the scheduling cell is 6 and theUL-DL subframe configuration of the scheduled cell is 4, Similarly, FIG.10 indicates that a UL-DL reference configuration of 6 may be used ifthe UL-DL subframe configuration of the scheduling cell is 3 and theUL-DL subframe configuration of the scheduled cell is 6, as shown in thetable of FIG. 8. Some combinations of FIG. 10, for example the use of aUL-DL reference subframe configuration of 1 if the UL-DL subframeconfiguration of the scheduling cell is 1 and the UL-DL subframeconfiguration of the scheduled cell is 4, correspond to both the tableof FIG. 8 and the method of FIG. 4.

Other embodiments may use fewer or different combinations of thereference UL-DL configuration, a UL-DL subframe configuration of ascheduling cell, and a UL-DL subframe configuration of a scheduled cellshown in FIG. 8 or 10, or derived from the method of FIG. 4. Theseembodiments may include additional combinations of a reference UL-DLconfiguration, a UL-DL subframe configuration of a scheduling cell, anda UL-DL subframe configuration of a scheduled cell not shown in FIG. 8or 10 or derived from the method of FIG. 4.

The eNB 104 and UE 108 described herein may be implemented into a systemusing any suitable hardware and/or software to configure as desired.FIG. 11 illustrates, for one embodiment, an example system 1100comprising one or more processor(s) 1104, system control logic 1108coupled with at least one of the processor(s) 1104, system memory 1112coupled with system control logic 1108, non-volatile memory(NVM)/storage 1116 coupled with system control logic 1108, and a networkinterface 1120 coupled with system control logic 1108.

Processor(s) 1104 may include one or more single-core or multi-coreprocessors. Processor(s) 1104 may include any combination ofgeneral-purpose processors and dedicated processors (e.g., graphicsprocessors, application processors, baseband processors, etc.). In anembodiment in which the system 1100 implements UE 108, processors(s)1104 may include processor module 152 and be configured to execute theembodiments of FIGS. 2-9 in accordance with various embodiments. In anembodiment in which the system 1100 implements eNB 104, processor(s)1104 may include processor module 128 and be configured to decode theHARQ ACK/NACK information transmitted by UE 108.

System control logic 1108 for one embodiment may include any suitableinterface controllers to provide for any suitable interface to at leastone of the processor(s) 1104 and/or to any suitable device or componentin communication with system control logic 1108.

System control logic 1108 for one embodiment may include one or morememory controller(s) to provide an interface to system memory 1112.System memory 1112 may be used to load and store data and/orinstructions, for example, for system 1100. System memory 1112 for oneembodiment may include any suitable volatile memory, such as suitabledynamic random access memory (DRAM), for example.

NVM/storage 1116 may include one or more tangible, non-transitorycomputer-readable media used to store data and/or instructions, forexample. NVM/storage 1116 may include any suitable non-volatile memory,such as flash memory, for example, and/or may include any suitablenon-volatile storage device(s), such as one or more hard disk drive(s)(HDD(s)), one or more compact disk (CD) drive(s), and/or one or moredigital versatile disk (DVD) drive(s), for example.

The NVM/storage 1116 may include a storage resource physically part of adevice on which the system 1100 is installed or it may be accessible by,but not necessarily a part of, the device. For example, the NVM/storage1116 may be accessed over a network via the network interface 1120.

System memory 1112 and NVM/storage 1116 may respectively include, inparticular, temporal and persistent copies of instructions 1124.Instructions 1124 may include instructions that when executed by atleast one of the processor(s) 1104 result in the system 1100implementing a one or both of methods 400 and 700 as described herein.In some embodiments, instructions 1124, or hardware, firmware, and/orsoftware components thereof, may additionally/alternatively be locatedin the system control logic 1108, the network interface 1120, and/or theprocessor(s) 1104.

Network interface 1120 may have a transceiver 1122 to provide a radiointerface for system 1100 to communicate over one or more network(s)and/or with any other suitable device. The transceiver 1122 may beimplement receiver module 144 and/or transmitter module 148. In variousembodiments, the transceiver 1122 may be integrated with othercomponents of system 1100. For example, the transceiver 1122 may includea processor of the processor(s) 1104, memory of the system memory 1112,and NVM/Storage of NVM/Storage 1116. Network interface 1120 may includeany suitable hardware and/or firmware. Network interface 1120 mayinclude a plurality of antennas to provide a multiple input, multipleoutput radio interface. Network interface 1120 for one embodiment mayinclude, for example, a network adapter, a wireless network adapter, atelephone modem, and/or a wireless modem.

For one embodiment, at least one of the processor(s) 1104 may bepackaged together with logic for one or more controller(s) of systemcontrol logic 1108. For one embodiment, at least one of the processor(s)1104 may be packaged together with logic for one or more controllers ofsystem control logic 1108 to form a System in Package (SiP). For oneembodiment, at least one of the processor(s) 1104 may be integrated onthe same die with logic for one or more controller(s) of system controllogic 1108. For one embodiment, at least one of the processor(s) 1104may be integrated on the same die with logic for one or morecontroller(s) of system control logic 1108 to form a System on Chip(SoC).

The system 1100 may further include input/output (I/O) devices 1132. TheI/O devices 1132 may include user interfaces designed to enable userinteraction with the system 1100, peripheral component interfacesdesigned to enable peripheral component interaction with the system1100, and/or sensors designed to determine environmental conditionsand/or location information related to the system 1100.

In various embodiments, the user interfaces could include, but are notlimited to, a display (e.g., a liquid crystal display, a touch screendisplay, etc.), a speaker, a microphone, one or more cameras (e.g., astill camera and/or a video camera), a flashlight (e.g., a lightemitting diode flash), and a keyboard.

In various embodiments, the peripheral component interfaces may include,but are not limited to, a non-volatile memory port, an audio jack, and apower supply interface.

In various embodiments, the sensors may include, but are not limited to,a gyro sensor, an accelerometer, a proximity sensor, an ambient lightsensor, and a positioning unit. The positioning unit may also be partof, or interact with, the network interface 1120 to communicate withcomponents of a positioning network, e.g., a global positioning system(GPS) satellite.

In various embodiments, the system 1100 may be a mobile computing devicesuch as, but not limited to, a laptop computing device, a tabletcomputing device, a netbook, a mobile phone, etc. In variousembodiments, system 1100 may have more or less components, and/ordifferent architectures.

Although certain embodiments have been illustrated and described hereinfor purposes of description, a wide variety of alternate and/orequivalent embodiments or implementations calculated to achieve the samepurposes may be substituted for the embodiments shown and describedwithout departing from the scope of the present disclosure. Thisapplication is intended to cover any adaptations or variations of theembodiments discussed herein. Therefore, it is manifestly intended thatembodiments described herein be limited only by the claims and theequivalents thereof.

What is claimed is:
 1. A method comprising: transmitting, from anenhanced NodeB (eNB), an indication of an uplink/downlink (UL-DL)subframe configuration of a scheduling cell in a wireless time-divisionduplex (TDD) system utilizing cross-carrier scheduling; transmitting anindication of a UL-DL subframe configuration of a scheduled cell in thewireless TDD system; identifying a type of the UL-DL subframeconfiguration of the scheduling cell based on an uplink round trip time(RTT) of a hybrid automatic repeat request (HARQ) process utilizing theUL-DL subframe configuration of the scheduling cell; and determining aHARQ timing configuration of the scheduled cell based on the type of theUL-DL subframe configuration of the scheduling cell.
 2. The method ofclaim 1, wherein the scheduling cell is a primary serving cell or asecondary serving cell, and the scheduled cell is a secondary servingcell.
 3. The method of claim 1, wherein determining further comprises:determining that the timing configuration is the UL-DL subframeconfiguration of the scheduling cell if the type is a first type that isassociated with an uplink HARQ RTT equal to 10 milliseconds; anddetermining that the timing configuration is the UL-DL subframeconfiguration of the scheduled cell if the type is a second type that isassociated an uplink HARQ RTT not equal to 10 milliseconds.
 4. Themethod of claim 1, wherein the HARQ process comprises transmitting,based on the timing configuration, a positive or negativeacknowledgement signal in the scheduling cell through at least onedownlink subframe of the scheduling cell, the positive or negativeacknowledgement signal being transmitted in a subframe of a physicalhybrid-ARQ indicator channel (PHICH).
 5. The method of claim 1, whereinthe UL-DL subframe configuration of the scheduled cell and the UL-DLsubframe configuration of the scheduling cell correspond to at least oneof TDD UL-DL configurations 0-6 associated with a 3^(rd) GenerationPartnership Project (3GPP) long-term evolution (LTE) advanced wirelesscommunication standard; and transmitting the indication of the UL-DLsubframe configuration of the scheduled cell comprises transmitting a3GPP LTE wireless communication standard system information block 1(SIB1).
 6. A user equipment (UE) comprising: a receiver configured toreceive respective indications of UL-DL subframe configurations of ascheduling cell and a scheduled cell in a wireless time-division duplex(TDD) system utilizing cross-carrier scheduling, the respective UL-DLsubframe configurations being different from one another; and aprocessor coupled with the receiver and configured to determine ascheduled cell timing configuration based at least in part on an uplinkround trip time (RTT) of a hybrid automatic repeat request (HARQ)process utilizing the UL-DL subframe configuration of the schedulingcell; wherein the receiver is further configured to receive a HARQsignal of the scheduled cell in at least one downlink subframe of thescheduling cell according to the scheduled cell timing configuration. 7.The UE of claim 6, wherein the scheduling cell is a primary serving cellor a secondary serving cell, and the scheduled cell is a secondaryserving cell.
 8. The UE of claim 6, wherein the HARQ signal comprises apositive or negative acknowledgement signal transmitted in a downlinksubframe of a physical hybrid ARQ indicator channel (PHICH).
 9. The UEof claim 6, wherein the scheduled cell timing configuration is the UL-DLsubframe configuration of the scheduling cell if the RTT is equal to 10milliseconds; and wherein the scheduled cell timing configuration is theUL-DL subframe configuration of the scheduled cell if the RTT is notequal to 10 milliseconds.
 10. The UE of claim 6, wherein the UL-DLsubframe configuration of the scheduled cell and the UL-DL subframeconfiguration of the scheduling cell are different ones of TDD UL-DLconfigurations 0-6 associated with a 3^(rd) Generation PartnershipProject (3GPP) long-term evolution (LTE) advanced wireless communicationstandard.
 11. The UE of claim 6, wherein the receiver is configured toreceive the UL-DL subframe configuration of the scheduled cell in a3^(rd) Generation Partnership Project (3GPP) long-term evolution (LTE)advanced wireless communication standard system information block 1(SIB1); and wherein the UE is a mobile phone, a netbook, a laptop, anelectronic tablet, or a data system of a vehicle.
 12. A systemcomprising: a receiver configured to receive, at a user equipment (UE),an indication of an uplink/downlink (UL-DL) subframe configuration of ascheduling cell in a wireless time-division duplex (TDD) systemutilizing cross-carrier scheduling; the receiver further configured toreceive an indication of a UL-DL subframe configuration of a scheduledcell in the wireless TDD system, the UL-DL subframe configuration of thescheduled cell being different from the UL-DL subframe configuration ofthe scheduling cell; and a processor configured to identify a referenceUL-DL subframe configuration based at least in part on the UL-DLsubframe configurations of the scheduling cell and scheduled cell; andwherein the receiver is further configured to receive, from thescheduling cell of an enhanced NodeB (eNB), a hybrid automatic repeatrequest (HARD) signal of the scheduled cell according to a subframetiming of the reference UL-DL subframe configuration.
 13. The system ofclaim 12, wherein: the reference UL-DL subframe configuration is equalto 1 if the UL-DL subframe configuration of the scheduling cell is equalto 1 and the UL-DL subframe configuration of the scheduled cell is equalto 2, 4, or 5; the reference UL-DL subframe configuration is equal to 2if the UL-DL subframe configuration of the scheduling cell is equal to 2and the UL-DL subframe configuration of the scheduled cell is equal to5; the reference UL-DL subframe configuration is equal to 3 if the UL-DLsubframe configuration of the scheduling cell is equal to 3 and theUL-DL subframe configuration of the scheduled cell is equal to 4 or 5;and the reference UL-DL subframe configuration is equal to 4 if theUL-DL subframe configuration of the scheduling cell is equal to 4 andthe UL-DL subframe configuration of the scheduled cell is equal to 5.14. The system of claim 12, wherein: the reference UL-DL subframeconfiguration is equal to 6 if the UL-DL subframe configuration of thescheduling cell is equal to 1, 2, 3, or 4, and the UL-DL subframeconfiguration of the scheduled cell is equal to 6; the reference UL-DLsubframe configuration is equal to 0 if the UL-DL subframe configurationof the scheduling cell is equal to 3 or 4, and the UL-DL subframeconfiguration of the scheduled cell is equal to 0; and the referenceUL-DL subframe configuration is equal to 1 if the UL-DL subframeconfiguration of the scheduling cell is equal to 4 and the UL-DLsubframe configuration of the scheduled cell is equal to
 1. 15. Thesystem of claim 12, wherein: the reference UL-DL subframe configurationis equal to 3 if the UL-DL subframe configuration of the scheduling cellis equal to 2 and the UL-DL subframe configuration of the scheduled cellis equal to 3; and the reference UL-DL subframe configuration is equalto 4 if the UL-DL subframe configuration of the scheduling cell is equalto 2 and the UL-DL subframe configuration of the scheduled cell is equalto
 4. 16. The system of claim 12, wherein: the reference UL-DL subframeconfiguration is equal to 0 if the UL-DL subframe configuration of thescheduling cell is equal to 6 and the UL-DL subframe configuration ofthe scheduled cell is equal to 0; the reference UL-DL subframeconfiguration is equal to 1 if the UL-DL subframe configuration of thescheduling cell is equal to 0 or 6, and the UL-DL subframe configurationof the scheduled cell is equal to 1, 2, or 5; the reference UL-DLsubframe configuration is equal to 3 if the UL-DL subframe configurationof the scheduling cell is equal to 0 or 6, and the UL-DL subframeconfiguration of the scheduled cell is equal to 3; the reference UL-DLsubframe configuration is equal to 6 if the UL-DL subframe configurationof the scheduling cell is equal to 0 and the UL-DL subframeconfiguration of the scheduled cell is equal to 6; and the referenceUL-DL subframe configuration is equal to 4 if the UL-DL subframeconfiguration of the scheduling cell is equal to 6 and the UL-DLsubframe configuration of the scheduled cell is equal to
 4. 17. Thesystem of claim 12, wherein the scheduling cell is a primary servicecell or a secondary serving cell; and wherein the scheduled cell is asecondary serving cell.
 18. The system of claim 12, wherein the receiveris further configured to receive an identification of the referenceUL-DL subframe configuration via radio resource control (RRC) signaling.19. The system of claim 12, wherein the processor is further configuredto identify the reference UL-DL subframe configuration via a tablestored in a memory of the UE.
 20. The system of claim 12, wherein atleast one of the UL-DL subframe configuration of the scheduled cell, theUL-DL subframe configuration of the scheduling cell, and the referenceUL-DL subframe configuration correspond to one of TDD UL-DLconfigurations 0-6 associated with 3^(rd) Generation PartnershipProject's (3GPP's) long-term evolution (LTE) advanced wirelesscommunication standard; and wherein the system is a mobile phone, anetbook, a laptop, an electronic tablet, or a data system of a vehicle.21. The system of claim 12, wherein the reference UL-DL subframeconfiguration is different from the UL-DL subframe configuration ofeither the scheduling cell or the scheduled cell.
 22. The system ofclaim 12, wherein the receiver is further configured to receive the HARQsignal of the scheduled cell in a downlink subframe of the schedulingcell; and wherein the HARQ signal comprises a positive or negativeacknowledgement signal.
 23. An enhanced NodeB (eNB) comprising: aprocessor configured to: determine respective uplink/downlink (UL-DL)subframe configurations of a scheduling cell and a scheduled cell in awireless time-division duplex (TDD) system utilizing cross-carrierscheduling, the UL-DL subframe configuration of the scheduled cell beingdifferent from the UL-DL subframe configuration of the scheduling cell;and determine a reference UL-DL subframe configuration based at least inpart on the UL-DL subframe configurations of the scheduling cell and thescheduled cell; and a transmitter configured to transmit to a userequipment (UE): an indication of the UL-DL subframe configuration of thescheduling cell; an indication of the UL-DL subframe configuration ofthe scheduled cell; and an indication of the reference UL-DL subframeconfiguration; wherein the transmitter is further configured to transmita hybrid automatic repeat request (HARQ) signal comprising a positive ornegative acknowledgement signal of the scheduled cell in a downlinksubframe of the scheduling cell.
 24. The eNB of claim 23, wherein theindication of the reference UL-DL subframe configuration is transmittedin radio resource control (RRC) signaling.
 25. The eNB of claim 23,wherein the scheduling cell is a primary service cell or a secondaryserving cell; and wherein the scheduled cell is a secondary servingcell.
 26. The eNB of claim 23, wherein at least one of the UL-DLsubframe configuration of the scheduled cell, the UL-DL subframeconfiguration of the scheduling cell, and the reference UL-DL subframeconfiguration are one of TDD UL-DL configurations 0-6 associated with3^(rd) Generation Partnership Project's (3GPP's) long-term evolution(LTE) advanced wireless communication standard.
 27. The eNB of claim 23,wherein: the reference UL-DL subframe configuration is equal to 1 if theUL-DL subframe configuration of the scheduling cell is equal to 1 andthe UL-DL subframe configuration of the scheduled cell is equal to 2, 4,or 5; the reference UL-DL subframe configuration is equal to 2 if theUL-DL subframe configuration of the scheduling cell is equal to 2 andthe UL-DL subframe configuration of the scheduled cell is equal to 5;the reference UL-DL subframe configuration is equal to 3 if the UL-DLsubframe configuration of the scheduling cell is equal to 3 and theUL-DL subframe configuration of the scheduled cell is equal to 4 or 5;the reference UL-DL subframe configuration is equal to 4 if the UL-DLsubframe configuration of the scheduling cell is equal to 4 and theUL-DL subframe configuration of the scheduled cell is equal to 5; thereference UL-DL subframe configuration is equal to 6 if the UL-DLsubframe configuration of the scheduling cell is equal to 1, 2, 3, or 4,and the UL-DL subframe configuration of the scheduled cell is equal to6; the reference UL-DL subframe configuration is equal to 0 if the UL-DLsubframe configuration of the scheduling cell is equal to 3 or 4, andthe UL-DL subframe configuration of the scheduled cell is equal to 0;the reference UL-DL subframe configuration is equal to 1 if the UL-DLsubframe configuration of the scheduling cell is equal to 4 and theUL-DL subframe configuration of the scheduled cell is equal to 1; thereference UL-DL subframe configuration is equal to 3 if the UL-DLsubframe configuration of the scheduling cell is equal to 2 and theUL-DL subframe configuration of the scheduled cell is equal to 3; thereference UL-DL subframe configuration is equal to 4 if the UL-DLsubframe configuration of the scheduling cell is equal to 2 and theUL-DL subframe configuration of the scheduled cell is equal to 4; thereference UL-DL subframe configuration is equal to 0 if the UL-DLsubframe configuration of the scheduling cell is equal to 6 and theUL-DL subframe configuration of the scheduled cell is equal to 0; thereference UL-DL subframe configuration is equal to 1 if the UL-DLsubframe configuration of the scheduling cell is equal to 0 or 6, andthe UL-DL subframe configuration of the scheduled cell is equal to 1, 2,or 5; the reference UL-DL subframe configuration is equal to 3 if theUL-DL subframe configuration of the scheduling cell is equal to 0 or 6,and the UL-DL subframe configuration of the scheduled cell is equal to3; the reference UL-DL subframe configuration is equal to 6 if the UL-DLsubframe configuration of the scheduling cell is equal to 0 and theUL-DL subframe configuration of the scheduled cell is equal to 6; andthe reference UL-DL subframe configuration is equal to 4 if the UL-DLsubframe configuration of the scheduling cell is equal to 6 and theUL-DL subframe configuration of the scheduled cell is equal to 4.